This invention relates to a transmission electron microscope having an objective lens equipped with three magnetic pole pieces.
Analysis for a very narrow area in a thin crystalline specimen by using a transmission electron microscope is carried out as follows.
First, the electron microscope is operated at an electron microscope (EM) mode. In this EM mode, the collimated beam of electrons irradiates the comparatively wide area on a specimen, and the electron microscope image of the specimen is displayed on a fluorescent screen by adjusting an image forming lens system. And the specimen is moved by a specimen positioning means so that the desired point (or very narrow area) to be analyzed in the field of the electron microscope image is displayed on the center of the fluorescent screen.
Next, the operation mode is changed to a convergent beam electron diffraction (CBED) mode. In this CBED mode, the electron beam is converged at said vary narrow area on the specimen by adjusting a condenser lens system, and the diffraction pattern is formed on the fluorescent screen by adjusting the image forming lens system. Analysis of this diffraction pattern makes it possible to precisely analyze the crystal structure of the material, to identify the material name, and to determine the orientation of the crystalline material.
It is theoretically possible to change the EM and CBED modes only by adjusting the condenser lens system and image forming lens system respectively. However, in the conventional electron microscope in which the specimen is located in the midst of the objective lens field, adjustment of the focusing lens system is followed by the change in the condenser lens system. Accordingly, it is further necessary to shift the specimen position along the optical axis for changing said EM and CBED modes. This operation of specimen shift is troublesome and requires some prudence and long operation time.
An object of the invention is to provide a transmission electron microscope capable of overcoming the above disadvantages so as to facilitate the change of the EM and CBED modes without specimen shift.